Resistor composition and devices embodying same



Feb. l5, 1966 w. E. coUN-rs l-:TAL 3,235,655

RESISTOR COMPOSITION AND DEVICES EMBODYING SAME Original Filed March 14, 1960 United States Patent O 3,235,655 RESHSTR COMPOSITHGN AND DEVICES EMBUDYNG SAME Wiiliam Edward Counts, Anaheim, Calif., Robert W. Smith, Flint, and Karl Schwartzwalder, Holly, Mich., assignors to Generai Motors Corporation, Detroit,

Mich., a corporation of Delaware Continuation of application Ser. No. 14,748, Mar. 14, 1960. This application Dec. 31, 1962, Ser. No. 248,307

19 Claims. (Ci. 174-152) This application is a continuation of our application Serial No. 14,748, filed Mar. 14, 1960, now abandoned.

This invention relates to resistor compositions and particularly to glass phase semiconductor resistor compositions suitable for use in resistors and resistor spark plugs of the automotive and aviation type and to the devices embodying such compositions.

Our invention is an improvement over the monolithic resistor plug described and claimed in the McDougal et al. Patent 2,459,282 granted Ian. 18, 1949. This patent discloses a resistance element comprising a heterogenous mixture of conductor material, i.e., carbon either alone or in combination with various conducting metals, metal oxides and metal carbides, with glass. In this composition, the conducting material exists as a continuous phase and the resistance thereof is dependent solely on the amount of conductor material present, the glass serving only to suspend the conductor material in a rigid structure. Such resistors are limited to relatively low temperature use due to flash-over and are relatively unstable electically.

Our invention is also an improvement over that described and claimed in the Counts et al. Patent 2,864,884 granted Dec. 16, 1958 which discloses and claims the stanno-titanate type semiconductor in glass phase. The patented compositions and resistor devices are not satisfactory for use where specification requirements are so strict as to approach the electrical stability characteristics of graphite.

It is therefore an object of our invention to provide a resistor composition having stable electrical characteristis. It is another object of our invention to provide a resistor element capable of withstanding high operating temperatures and having stable electrical characteristics. It is another object of our invention to provide a spark plug having stable electrical characteristics and capable of withstanding high operating temperatures.

To attain these objects we provide a resistor semiconductor material comprising a sintered binary composition of metal oxides in admixture with glass with the addition of small amounts of reducer material, the mixture being hot-pressed to form a non-porous resistor element having a gas tight sealing bond with the containing insulator body.

Further objects and advantages lof the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of our invention is clearly shown.

In the drawing:

FIGURE l is a vertical cross-sectional view of an automotive type spark plug embodying our invention.

FIGURE 2 is a section `through a resistor suitable for use in an aviation type ignition harness.

Having reference to FIGURE 1 there is shown an automotive type spark plug 1 comprising a shell 3 provided with screw threads at its lower end for threaded connection with the engine, a ground electrode 5 being secured to its lower edge. The shell 3 is provided with a stepped centerbore '7 forming an internal ledge 9 therein. Positioned on the ledge 9 is an insulator sleeve 117 formed ice preferably of sintered aluminum oxides, other type materials being possible, the insulator being secured in gas tight relationship with the shell 3.

The insulator 11 is provided with a stepped centerbore 13 adapted to receive and position a center electrode 15 on the ledge 17 formed therein. The electrode 15 may be formed of any suitable material capable of withstanding high temperatures and possessing good heat conductivity. Positioned in the centerbore and overlying the electrode 15 is the resistor section 19. The section 19 has good electrical contact with the electrode 15 and is in gas tight sealed relationship within the insulator 11. The resistor section 19 comprises a lower conducting seal 23, an upper conducting seal 25 and an intermediate portion 27 constituting the resistor composition of oui invention. The conducting seals may be made of any suitable material capable of being bonded to the insulator and to the resistance element and possessing good electrical conductivity. We prefer to use a mixture of glass and conducting material as described and claimed in Schwartzwalder and Kirk Patent 2,106,578 granted lan. 25, 1938, and Schwartzwalder and Rulka Patent 2,248,415 granted July 8, 1941.

The lower seal 23 is subjected to greater heating during operation of the plug than is the upper seal 31 and is preferably made from a mixture by boro-silicate glass and powdered copper, the plasticity thereof being such as to preclude its running down over the lower surfaces of the center electrode 15 during the hot pressing operation. The upper seal 25 is formed of a lower portion 29 and an upper portion 31, the lower portion 29 being relatively stiff on hot pressing in order to serve as a plunger for evenly compressing the intermediate portion 27. Both sections 29 and 31 are likewise formed of a mixture comprising powdered copper in glass.

In an effort to find a resistor composition satisfying rigid specications limiting variation in resistance over the temperature and voltage range encountered in normal operation as well as one capable of withstanding temperatures as high as 1000 F., we have discovered a series of semiconductor materials which are sintered binary compositions of metal oxides which, when reacted with a glass phase and reducer material, produce semiconductor compositions having stable and reproducible electrical characteristics, i.e., low temperature coefficient of resistivity and low voltage coeiiicient of resistivity.

More specifically, in order to meet rigid military requirements, extended testing and development resulted in the discovery that the required electrical stability was obtained by use of sintered titanium-zirconates, TiO2=ZrO2, and the sintered binary compositions of tantalum oxide and cerium oxide, thorium oxide and didymium oxide. As used herein and as available commercially, didymium oxide consists essentially of the following constituents in about the percent by weight stated:

45.5% lanthanum oxide La2O3 38.0% neodymium oxide Nd203 11.0% praseodymium oxide PrOu 4.0% samarium oxide Sm2O3 1.5% of other rare earth oxides.

found that suitable calcines are formed of mixtures consisting essentially of about 5 `to 15% by weight Ta2O5 and 85 to 95% of thorium, cerium or didyrnium oxide, the preferred mixture being about TaZO and 90% of the other oxide. Similarly, suitable calcines of TOZ and ZrO2 may be formed using mixtures of about 0.5 to 60% by weight TiOZ and 40 to 99.5% ZrO2, the preferred mixture being about 10% by weight TiO2 and 90% ZrOz.

Within the range stated, the variation of tantala causes little change in ythe temperature and voltage coeflicients of resistivity. With reference to the semiconductor compositions using the titania-zirconia system of binary calcines, we have found the temperature and voltage coefficients of resistance to be about 50% less than those of the stanno-titanate compositions disclosed in our Patent 2,864,884. It has also been found that Where TiO2 is present in amounts more than about 60% by weight, the semiconductor composition will have the electrical properties of TiO2, i.e., higher temperature and voltage coefficients of resistance than those -within the stated range. Shown in Table l are the temperature and voltage coefficients of resistance found for the semiconductor materials of our invention when embodied in spark plugs of the type shown in FIGURE l as the glass-pbase compositions described hereinafter.

As used herein, the temperature coeflicient of resistance test consists of measuring the centerwise resistance of the insulator assembly at 80 IF., then im-mersing the system in a temperature-controlled oil bath at 350 F., `and Aagain measuring the centerwise resistance. The temperature coeflicient is expressed as the ratio of resistance at 350 F. to resistance at 80 F.

The voltage coefcien-t of resistance test consists of measuring the centerwise resistance of an insulator assembly lat different voltages. The voltage coefficient is expressed as the ratio of the resistance at 5 kv. to the resistance at 3 volts.

In forming the insulator assemblies described, the resistor glass seal was achieved by loading the semiconductor `glass-phase composition into the insulator between layers of copperagla'ss contact seal material and beating to the :temperature where the reducing material reacts to develop the desired stable electrical properties. It has been `found satisfactory to heat rapidly to about 1620 to 1650 F. and soak for about 5 minutes after which the glass-phase layers are cooled Iwhile under pressure to form a dense compact body, The time periods are not critical since it is merely necessary to raise the materials to an elevated temperature to enable reaction and Softening of the glass for hot pressing.

We have found that the semiconductor glass phase compositions of our invention may be formed of the -following constituents in the percent by weight noted:

Percent Glass 5-40 Semiconductor material 35-90 nert liller-kyanite, borolon, Zircon, mullite,

etc. 0-25 Binderclay (bentonite), -animal glue 0-3 Reducing materialcarbon-ace-tylene black,

graphite, etc. 0.1-3

With specific reference to the titania-Zirconia system, the `following range of constituents produces the compositions having the greatest ease of handling yas granules of about 28 mesh size and having the most stable electrical properties, a specific preferred composition being in about the percent by weight noted.

With reference to the several constituents called for, the most uniform resistances and reproducible electrical properties (such as temperature coeflicient of resistance and voltage coeicient of resistance) have been obtained with a barium borate glass yas the glass phase. When an ordinary soda-lime-silica glass, fboric anhydride, barium boro-silicate glass or lead boro-silicate glass is substituted for the barium borate glass, the electrical resistance increases greatly and is therefore outside the desired resistance range of 15,000 ohms maximum Iat 5 kv. and room temperature. The kyanite acts only as an inert filler and can be substituted for by any inert grog, such as borolon grain, mullite, Zirconia, etc. The acetylene black (carbon) is added to create a reducing atmosphere during the hot pressing operation; by adding a certain amount of this material, the semiconductor material is reduced a very definite amount, so that semiconduction by holes -and/or by electrons occurs. We can control the resistance range of the glass seal `by means of the reducing agent. The bentonite is an inert inorganic binder which aids in the granulating process but does not affect the electrical properties. Certain organic binders, on decomposing at the glass temperature, leaves behind a carbon residue wh-ich causes additional (and uncontrollable) reduction of the semiconductor. A few or- Vg-anic binders, notably those made of animal glues, are actually better lglass seal granule binders, but are slightly inferior to bentonite-bonded seals Ifor electrical properties. With `specific reference to the titania-zirconia system, we have found it necessary to use zirconia of the highest purity, i.e., at least 99.7% .pure whereas the titania may be of the commercial non-ohalking paint tgrade. Also, as used herein, the barium-borate glass consists essentially of about 25% by weight BaO2 and With specific reference to the tantala metal oxide systems, the following is a preferred composition in about the percent by weight noted, the remarks made above being equally yapplicable thereto:

Percent Glass-barium `borate 33 Semiconductor material 38 Inert liller-kyanite 25 Binder-bentonite 3 Carbon-acetylene black 2 The semiconductor glass phase compositions of our invention may be prepared in glanular form by first dry mixing the materials and then adding water to make a plastic mass. The plast-ic mass is then forced through a 20 mesh screen and the resulting `granules dried. The dried material is then regranulated through a 28 mesli `screen and the material retained between 28 and mesh is used. This sizing has been found to produce lgranules which are most suitable for uniform volumetric feed. Alternatively, the materials may be dry mixed and formed into a free-flowing slip by addition of water. The slip is `then passed into a spray-drying tower where the desired agglcmerates are formed.

In assembling the plug 1, the center electrode 1S is positioned within the centerbore 13 of the insulator 11 and a measured amount of copper-glass seal is fed into the bore and rammed in place. Any loose powder is blown out of the insulator to prevent contamination of the intermediate resistor portion 27. The desired amount of powdered semi-conductor composition is then placed in the bore and rammed, followed by a measured amount of powdered copper-glass seal material 29 which is likewise rammed to form the lower portion 29 of the upper conducting seal 25. A small quantity of copper-glass material is then loaded into the insulator followed by ramming to form the upper portion 31 of conducting seal 25. A terminal screw 33 is then positioned within the bore and the whole assembly is heated to a temperature enabling reaction of the reducer with the metal oxides and glass softening, a temperature of about 16.20 to l650 F. being generally satisfactory. When the glass is sufficiently softened, pressure is applied to the terminal screw 33 to force it down into the bore, thereby compressing the softened materials and causing the upper seal portion 31 of upper seal 25 to surround and grip the lower end of the screw. By hot-pressing in this manner, a continuous electrical path is formed through the plug from the terminal screw 33 to the center electrode 15, the portions intermediate the top of the electrode and the bottom of the screw being sealed in gas tight relationship with the wall of the insulator and the metal parts. The thus formed insulator assembly is then assembled in shell 3 to form plug 1.

In FIGURE 2 there is shown a resistor 41 embodying the resistor element of our invention. The resistor 41 consists of an insulator sleeve 43 of either sintered alumina or porcelain, as in the case of insulator 11, having a resistor section 45 comprising a lower conductive seal 47, an intermediate resistor portion 51 and an upper conducting seal 49, likewise as shown and described with reference to FIGURE 1. Secured within the ends of the glass seals 47 and 51 are a pair of metal terminals 53, each of which is connected to an ignition cable 55 in the ignition harness or other electrical circuit. The cables 55 are secured within the terminals 53 in any suitable manner well known in the art. The glass seals 47 and 49 Aform a good electrical bond with the terminal 53 in a manner similar to that shown and described with reference to FIGURE 1.

The method of manufacture of this resistor 41 is substantially the same as that described above for plug 1. One of the terminals 53 is inserted in the sleeve 43, the glass seal material is inserte-d, followed by the powdered resistance material and the second seal material. The other terminal 53 is then inserted and the assembly is heated to soften the glass, pressure being then applied to the terminals to cause them to seat in the glass as shown and to compress the conducting seals and the resistance portion 47, 51 and 49, respectively.

As fully described above, we have provided binary metal oxide semiconductor glass seal resistor compositions and spark plugs and resistors embodying same which comply `with severe military requirements that the resistance at room temperature and at 5000 volts be from 7500- 15,000 ohms and that at 45 F.i5 F. and 5000 volts the resistance be from 5000-17,500 ohms. It should be noted that the materials and compositions disclosed by applicants are such that they are not susceptible of precise description after tiring and hot pressing other than by reference to their treatment since they form inter-crystalline structures of a complex nature. While other embodiments may be apparent to those skilled in the art, such embodiments are within the scope of our invention as set forth in the following claims.

We claim:

1. A composition of matter formed from a mixture consisting essentially of 5-40% barium-borate glass, 35-90% sintered semiconductor material, 0-25% inert filler, -3% binder and 0.1-3% carbon as a reducing agent, said semiconductor material being selected from the binary metal oxide systems consisting of TiO2-ZrO2, Ta2O5-Th02, Ta2O5-Ce02 and Ta2O5-Di02 wherein the TiO2 and ZrO2 in said titania system are present 1n an amount of about 0.5 to 60% and 40 to 99.5% by welght,

respectively, and the Ta205 and the other metal oxide in said tantala systems are present in an amount of about 5 to 15% and 85 to 95% by weight, respectively, said ZrOZ being at least 99.7% by weight pure, said Di02 consisting essentially of about 45.5% by weight lanthanum oxide, about 38.0% by weight neodymium oxide, about 11.0% praseodymium oxide, about 4.0% samarium oxide and about 1.5% other rare earth oxides.

2. A composition of matter as set forth in claim 1 wherein the TiO2 and ZrO2 are present in an amount of about 10% and 90% by weight, respectively, and the Ta2O5 and the other metal oxides are present in an amount of about 10% and 90% by weight, respectively, said semiconductor material having been sintered at a temperature of from about 2300 F. to about 2950 F.

3. A composition of matter formed from a mixture consisting essentially of 13-32% barium-borate glass, 5777% TiO2-Zr02 semiconductor material which has been fired to sintering temperature, 7.5-11% inert filler, 0.75-1.1% binder and 0.1-3% carbon, said TiO2 and ZrOi, being present, respectively, in an amount of about 0.5 to 60% by weight and 40 to 99.5% by weight and said ZrO2 being at least 99.7% by weight pure.

4. A composition as set forth in claim 3 wherein said TiO2 and ZrO2 are present, respectively, in an amount of about 10% and 90%, said semiconductor material having been sintered at a temperature of from about 2300 F. to about 2950 F.

5. A composition of matter formed from a mixture consisting essentially of about 13.3% barium-borate glass, about 75.6% TiO2-Zr02 semiconductor material, 8.8% inert filler, 0.9% binder and 1.4% carbon, said TiO2 and ZrO2 being present, respectively, in an amount of about 10% and 90% and said ZrOZ being at least 99.7% by Weight pure, and said semiconductor material having been sintered at a temperature of from about 2300 F. to about 2950 F.

6. A composition of matter formed from a mixture consisting essentially of about 33% barium-borate glass, about 38% sintered semiconductor material Ta2O5-Ce02, about 25% inert ller, about 3% binder and 2% carbon, said Ta2O5 in the semiconductor material being present in an amount of about 10%, said semiconductor material having been sintered at a temperature of from about 2300 F. to about 2950 F.

7. A composition as set forth in claim 6 wherein said semiconductor material is Ta2O5-Th02.

8. A composition as set forth in claim 6 wherein said semiconductor material is Ta2O5-Di02, said DiO2 consisting essentially of about 45.5 by weight lanthanum oxide about 38.0% by weight neodymium oxide, about 11.0% praseodymium oxide, about 4.0% vsa-marium oxide and about 1.5 other rare earth oxides.

9. A resistance ele-ment having stable electrical properties formed from `a composition consisting essentially of 5-40% glass, 35-90% semiconductor material which has been tired to -sintering temperature, 025% inert ller, 0-3% binder and 0.1-3% reducing agent, said semiconductor material being selected from the binary metal oxide systems consisting of TiO2-Zr02, Ta2O5-Th02, T'a2O5-Ce02 and Ta2O5-Di02 wherein the TiO2 and ZrOZ in said titania system are present in an amount of about 0.5 to 60% and 40 to 99.5% by weight, respectively, and the Ta205 and the other metal oxide in said tantala systems are present in an amount of about 5 to 15% and 85 to 95% by weight, respectively, said ZrO2 being at least 99.7% by weight pure, said composition having lbeen heated to a temperature at which the reducing agent reacts to develop the desired sta-ble electrical properties, said DiO2 consisting essentially of about 45.5% by weight lanthanum oxide, about 38.0% by weight neodymium oxide, about 11.0% praseodymium oxide, about 4.0% samarium oxide and about 1.5% other rare earth oxides.

10. A resistance element as set yforth in claim 9 wherein said glass is a barium-borate glass and wherein the Ti02 and ZrOZ are present in an amount of about 10% and 90% by Weight, respectively, and the Ta205 and the other metal oxides are present in an am-ount of about 10% .and 90% by Weight, respectively, said composition having been heated to a temperature of from about 1620 F. to about 1650 F.

11. A `resistance element having stable electrical properties formed from a composition of matter consisting essentially of 13-32% barium-borate glass, 5777% TiO2-ZrO2 semiconductor material which has been red to sintering temperature, 7.5-11% inert l'ler, 0.75-1.1% binder and 0.1-3% carbon, said TOZ and Z102 being present, respectively in an amount of about 0.5 to 60% by Weight and 40 to 99.5% by Weight and said ZrOZ being at least 99.7% by Weight pure, said composition having been heated to a temperature at which the reducing agent reacts to develop the desired stable electrical properties.

12. A resistance element having stable electrical propcrt-ies formed from a composition of matter consisting essentially of about 13.3% barium-berate glass, about 75.6% TiO2-Z1O2 semiconductor material sintered at a temperature of from about 2300 F. to about 2950 F., 8.8% inert filler, 0.9% binder .and 1.4% carbon, said TiO2 and ZrO2 are present, respectively, in an amount of about 10% and 90%, and sa-id ZrO2 being at least 99.7% by Weight pure, said composition having been heated to a temperature of from about 1620" F. to about 1650 F.

13. A resistance element having stable electrical properties formed from a composition of matter on a Weight basis consisting of about 33% barium-borate glass, about 38% semiconductor material Ta2O5-Ce02 sintered at a temperature of from about 2300 F. to about 2950 F., about 25% inert ller, about 3% binder and 2% carbon, said Ta2O5 in the semiconductor material being present in an amount of about 10%, said composition havin-g been heated to a temperat-ure of from about 1620 F. to about 1650 F., and cooled under pressure to form a dense compact body. p.

14. A resistor comprising the combination of a tubular insulator sleeve, a metal conducting member positioned in said sleeve, a glass conducting seal overlying said member and having a `gas-tight bond with said sleeve, a semiconductor overlying said seal and being bonded thereto and to said sleeve, a second glass conducting seal overlying said semiconductor and being bonded thereto and to said sleeve, and a second metal conducting member in said sleeve having ygood electrical connection with said second seal, said semiconductor .being formed from a composition of matter consisting essentially of 13-32% barium-borate glass, 57-77% TiO2-Zr02 semiconductor material which has been tired to sintering temperature, 7.5-11% inert filler 0.75-1.1% binder .and 0.1-3% canbon, said TiO2 and ZrOz lbeing present, respectively, in an amount of about 0.5 to 60% by Weight and 40 to 99.5% by Weight and said ZIOZ being at least 99.7% `by Weight pure, said composition :having .been heated Within said sleeve to a temperature at which the reducing agent reacts to develop the desired stable electrical properties.

15. A resistor comprising the combination of a tubular insulator sleeve, a metal conducting member positioned in .said sleeve, a glass conducting seal overlying said member and having a gas-tight -bond with said sleeve, a semiconductor overlying said seal and being .bonded thereto and to said sleeve, a second `glass conducting seal overlying said semiconductor and being bonded thereto and to said sleeve, and a second metal conducting member -in said sleeve having a `good electrical connection with said second seal, said semiconductor being formed from a composition consisting essentially of -40% glass, 35-90% semiconductor material which has been red to .sinterinig temperature, 0-25% inert ller, 0-3% binder and Oil-3% reducing agent, said semiconductor material being selected from the binary metal oxide systems consisting of TiO2- ZrO2, T a2O5-Th02, Ta2O5-Ce02 and Ta2O5-Di02 wherein the TiOz and ZrO2 in said titania system are present in an amount of .about 0.5 to 60% and 40 to 99.5% by Weight, respectively, and the Ta205 and the other metal oxide in said tantala systems are present in an amount of about 5 to 15% and 85 to 95% by weight, respectively, said ZrO2 being at least 99.7% by Weight pure, said composition having been heated Within said sleeve to a temperature at which the reducing agent reacts to develop the desired stable electrical properties, :said DiO2 consisting essentially of about 45.5 by Weight lanthanum oxide, about 38.0% by Weight neodymium oxide, about 11.0% praseodymium oxide, about 4.0% samarium oxide and about 1.5% other rare earth oxides.

16. A device comprising the combination of a tubular insulator, a metal conducting member positioned in said insulator, a semiconductor overlying said member in good electrical connection therewith and being bonded to said insulator, and a second metal conducting member in said insulator having good electrical connection with said semiconductor, said semiconductor being formed from a composition consisting essentially of from 35- 90% binary metal oxide semiconductor material Which has been tired to sintering temperature and is in admixture with 5-40% glass and 0.143% reducing agent, said semiconductor material being selected from the binary metal oxide systems consisting of TiO2-ZrO2, Ta2O5-Th02, Ta2O5-Ce02 and T a2O5-DiO2 wherein the TiO2 and Zr02 in said titania system are present in an amount of about 0.5 to 60% and 40 to 99.5% by Weight, respectively, and the Ta205 and the other metal oxide in said tantala systems are present in an amount of about 5 to 15% and to 95% by weight, respectively, said ZrO2 being at least 99.7% by weight pure, said composition having been heated Within said insulator to a temperature at which the reducing agent reacts to develop the desired stable electrical properties, said DiO2 consisting essentially of about 45.5% by Weight lanthanum oxide, about 38.0% by Weight neodymium oxide, about 11.0% praseodymium oxide, about 4.0% samarium oxide and about 1.5 other rare earth oxides.

17. A device comprising the combination of a spark plug insulator having a centerbore formed therein, a center electrode member positioned in said insulator, a glass conducting seal overlying said member and having a gas-tight bond with said insulator, a semiconductor overlying said seal and being bonded thereto and to said insulator, a second conducting seal overlying said semiconductor and being bonded thereto and to said insulator, and a terminal screw in said insulator having good electrical connection with said second seal, said semiconductor being formed from a composition of matter consisting essentially of about 13.3% barimum-borate glass, about '75.6% TiO2-Zr02 semiconductor material which has been fired to sintering temperature, 8.8% inert ller, 0.9% binder and 1.4% carbon, said TiO2 and ZrO2 are prese-nt, respectively, in an amount of about 10% and and said ZrOZ being at least 99.7% by Weight pure, said composition having been heated Within said insulator to a temperature at which the reducing agent reacts to develop the desired stable electrical properties.

18. A device comprising the combination of a spark plug insulator having a centerbore formed therein, a center electrode member positioned in said insulator, a glass conducting seal overlying said member and having a gas-tight bond with said insulator, a semiconductor overlying said seal and being bonded thereto and to said insulator, a second conducting seal overlying said semiconductor and being bonded thereto and to said insulator, and a terminal screw in said insulator having good electrical connection with said second seal, said semiconductor being formed from a composition of matter consisting of about 33% barium-borate glass, about 38% semiconductor material Ta2O5-Ce02 sin-tered at a temperature of from about 2300" F. to about 2950 F., about 25% inert ller, about 3% binder and 2% carbon, said Ta205 in the semiconductor material being Present in an heated to a temperature of from about 1620 F. to about 1650 F.

19. A device as set forth in claim 18 wherein said semiconductor material is Ta2O5-Di02, said DiOz consisting essentially of about 45.5% by Weight lanthanum oxide, about 38.0% by Weight neodymium oxide, about 11.0% praseodymium oxide, about 4.0% samarium oxide and about 1.5% other rare earth oxides.

References Cited by the Examiner UNITED STATES PATENTS Becker 252-57 XR McDougal et al. 252-507 Kilpatrick 106-47 XR Counts et al. 252-503 Counts et al. 174-152 Counts et al 252-520 JULIUS GREENWALD, Primary Examiner. 

15. A RESISTOR COMPRISING THE COMBINATION OF A TUBULAR INSULATOR SLEEVE, A METAL CONDUCTING MEMBER POSITIONED IN SAID SLEEVE, A GLASS CONDUCTING SEAL OVERLYING SAID MEMBER AND HAVING A GAS-TIGHT BOND WITH SAID SLEEVE, A SEMICONDUCTOR OVERLYING SAID SEAL AND BEING BONDED THERETO AND TO SAID SLEEVE, A SECOND GLASS CONDUCTING SEAL OVERLYING SAID SEMICONDUCTOR AND BEING BONDED THERETO AND TO SAID SLEEVE, AND A SECOND METAL CONDUCTING MEMBER IN SAID SLEEVE HAVING A GOOD ELECTRICAL CONNECTION WITH SAID SECOND SEAL, SAID SEMICONDUCTOR BEING FORMED FROM A COMPOSITION CONSISTING ESSENTIALLY OF 5-40% GLASS, 35-90% SEMICONDUCTOR MATERIAL WHICH HAS BEEN FIRED TO SINTERING TEMPERATURE, 0-25% INERT FILLER, 0-3% BINDER AND 0.1-3% REDUCING AGENT, SAID SEMICONDUCTOR MATERIAL BEING SELECTED FROM THE BINARY METAL OXIDE SYSTEMS CONSISTING OF TIO2ZRO2, TA2O5-THO2, TA2O5-CEO2 AND TA2O5-DIO2 WHEREIN THE TIO2 AND ZRO2 IN SAID TITANIA SYSTEM ARE PRESENT IN AN AMOUNT OF ABOUT 0.5 TO 60% AND 40 TO 99.5% BY WEIGHT, RESPECTIVELY, AND THE TA2O5 AND THE OTHER METAL OXIDE IN 